1. Field of the Invention
The present invention relates to a light-emitting device, and more particularly to a light-emitting device provided with a reflective frame for reflecting the light from a light-emitting chip.
2. Description of Related Art
Conventionally there are known light-emitting devices provided with a reflective frame (reflector) for reflecting the light radiated from a light-emitting chip (see, for example, JP-A-2005-229003).
JP-A-2005-229003 mentioned above deals with a light-emitting device provided with a metal reflector formed of a metal material with high thermal conductivity. According to JP-A-2005-229003, in the just-mentioned metal reflector formed of a metal material with high thermal conductivity, there are formed a light-emitting chip mount cavity portion, which forms a reflective surface, and a leg portion. The leg portion is secured on a mount circuit board, and this allows the heat conducted to the metal reflector to be conducted via its leg portion to the mount circuit board efficiently.
According to JP-A-2005-229003, however, the reflector is bonded via an adhesive layer to a printed circuit board on which a light-emitting chip is mounted. Generally the adhesive used to bond the metal reflector and the printed circuit board together is an adhesive based on resin such as epoxy resin. Since an adhesive based on resin such as epoxy resin has low thermal conductivity, it does not efficiently conduct the heat accompanying the light emission of the light-emitting chip from the printed circuit board to the metal reflector. Thus, according to JP-A-2005-229003, certainly the heat conducted to the metal reflector can be conducted to the mount circuit board efficiently but, due to a rate-determining factor, namely the adhesive layer bonding the metal reflector and the printed circuit board together, it is disadvantageously difficult to conduct the heat accompanying the light emission of the light-emitting chip from the printed circuit board to the metal reflector efficiently.
Moreover, the metal material of which the metal reflector is formed is easily oxidized. For example, when the metal reflector is formed of a metal material containing aluminum as its main content, since aluminum is an extremely easily oxidized material, the metal reflector is easily oxidized by oxygen in air, forming an oxide film on the surface. This oxidation of the surface of the metal reflector occurs naturally, and thus the thickness, shape, etc. of the oxide film formed are not uniform but nonuniform. With a nonuniform oxide film formed on the surface of the light-emitting chip mount cavity portion of the metal reflector in this way, when the cavity portion is sealed with sealing resin, low adhesion between the metal reflector and the sealing rein results, producing a gap between them. This causes variation in the reflection efficiency of the light emitted from the light-emitting chip, disadvantageously leading to low reliability.